A process for displacing sap from tree stems, patented by the applicant and assigned to HEW, has been used to produce extracts of which a remarkably large percentage have shown confirmed activity against cancer in the NCI cancer screen. Of 544 sap extracts of North American tree species 38 or 7% were active against P388 leukemia. 1499 Costarican tree sap extracts yielded 177 actives (12%). Extracts prepared by conventional methods from the same tree species have yielded only 1 or 2% actives. From one of the Costarican extracts a new potent antileukemic compound, Quassimarin, has been isolated by the fractionators. It is planned to continue searching for active drugs in the sap of Peruvian tree species but insofar as possible proceeding on a more rational program of collecting the tree stems based on the frequency of activity in various families as shown by previous work. So far the applicant has prepared his extracts by evaporation of the sap at 100 degrees C. He now also plans to selectively reprocess by freeze-drying saps that have shown activity, and all members of families that from the statistical data he has amassed so far, are indicated as potential sources of anti-cancer drugs.